The present invention relates to a method for judging road surface condition and a device thereof, and a program for judging road surface condition. More specifically, the present invention relates to a judging method of road surface condition which can improve the performance and running safety of a vehicle by judging the road surface and the abrasion condition of tires, and a device thereof; and a program for judging the road surface condition.
There have been conventionally proposed an antilock brake device and the like which lower braking torque which acts on wheels before braking force between tires and road surface exceeds a maximum value and the tires become in a lock condition, prevent the lock condition of wheels, and control the rotational number of wheels by which the maximum braking force is obtained (for example, Japanese Unexamined Patent Publication No. 99757/1985 and Japanese Unexamined Patent Publication No. 249559/1989). For example, the friction coefficient of the road surface, μ is utilized in the control of the antilock brake device, and an optimum control is designed to be carried out by changing the content of control in accordance with the friction coefficient of the road surface, μ (road surface, μ), for example, between a case of high μ and a case of low μ.
As the friction coefficient of the road surface-judging device which judges such road surface, μ, there is a device which determines a relation equation between a slip ratio and the acceleration or deceleration of a vehicle, and then judges the friction coefficient between the road surface and tires based on the slope of said relation equation (Japanese Unexamined Patent Publication No. 253334/2001). The road surface μ is designed to be judged by the threshold of a linear regression coefficient, K1 between a slip ratio and the acceleration or deceleration of a vehicle, for the slope.
However, since the threshold for judging the slipperiness of the road surface is preliminarily input from past data, it is required to input the threshold again when tires are replaced with the different kinds of tires.
Then, there are a road surface condition-judging device (Japanese Unexamined Patent Publication No. 274357/2002) in which after a correlative coefficient and the linear regression coefficient between a slip ratio and the acceleration or deceleration of a vehicle are determined, the threshold of judging the road surface condition is set based on the linear regression coefficient when said correlative coefficient is a fixed value or more, and a road surface condition-judging device (Japanese Unexamined Patent Publication No. 118555/2003) in which after the slip ratio of the front and rear wheels at left side to the front and rear wheels at right side and the slip ratio of the front and rear wheels are respectively calculated, the fluctuation quantity of difference of said left and right slip ratios is calculated, and then the threshold of judging the road surface condition is set based on the linear regression coefficient between the slip ratio of the front and rear wheels and the acceleration or deceleration of a vehicle when said fluctuation quantity is a fixed value, and the like.
Further, when tires are abraded, the thickness of tread rubbers of tires becomes thin, therefore the back and forth rigidity of a pattern becomes large. When tires are abraded, tires for winter affect performance on snow and tires for summer affect hydroplaning performance. Accordingly, it is also useful to detect the abrasion. For example, as a road surface condition-detecting device of judging that the abrasion of tires proceeds, there is a device (Japanese Unexamined Patent Publication No. 36837/2002) in which the abrasion of tires is designed to be detected by comparing the mutual linear regression coefficient between the slip ratio and the acceleration or deceleration of a vehicle with frequency distribution which is preliminarily grasped.